1. Field of the Invention
This invention relates to an auto-collimator.
The present application claims priority from Japanese Application No.2003-114518, the disclosure of which is incorporated herein by reference.
2. Description of the Related Art
Auto-collimators are used for various checks, tests, measurements, adjustments and regulations, e.g., a mounting check for optics such as a mirror, lens, prism and the like, a swinging or inclination check for a CD and a DVD, a mounting adjustment for the pickup of a CD apparatus or a DVD apparatus, an inclination adjustment of the optical axis in a laser diode (LD), an inclination check for a head of a hard disk drive (HDD), a measurement of parallelism between a charged-coupled device (CCD) and a cover glass, and measurements of inclination and parallelism for various planes such as in a surface plate, table, parts and the like.
FIG. 1 is a schematic block diagram of a conventional laser auto-collimator such as that described in Japan Examined Patent Publication No. 55-25605.
In FIG. 1, the auto-collimator 1 has a cover glass 3 fitted into an opening formed in the face at one end (the left-hand end in FIG. 1) of an approximately box-shaped casing 2, and a verification screen 4 attached to another opening formed in a side face close to the other end (the right-hand end in FIG. 1) of the casing 2.
The casing 2 houses a beam splitter 5, a convex lens 6 and a concave lens 7 fastened in this order from the cover glass 3 in mutually coaxial positions along an axis a parallel to the axis of the casing 2.
The concave lens 7 is situated in a position corresponding to the focal point of the convex lens 6.
A first reflection mirror 8 is fixed in a position intersecting with the axis a in the end portion of the casing 2 in the proximity of the verification screen 4 in such a way that the normal of the first reflection mirror 8 is inclined toward the opposite side from the verification screen 4 with respect to the axis a. Further, a second reflection mirror 9 is fixed opposite to the verification screen 4 in such a way as to be inclined toward the first reflection mirror 8 with respect to the normal of the verification screen 4.
The inclination angles of the normals of the first reflection mirror 8 and the second reflection mirror 9 are determined respectively at angles allowing the light passing from the cover glass 3 through the beam splitter 5, convex lens 6 and concave lens 7 to be reflected by the first reflection mirror 8 and the second reflection mirror 9 in order to enter the verification screen 4, which will be described later.
A light source S having a laser diode is mounted opposite the beam splitter 5 inside the casing 2 and oriented to apply and position a laser beam L onto the beam splitter 5.
In the auto-collimator 1, a laser beam L emitted from the light source S is reflected at right angles by the beam splitter 5, and then passes through the cover glass 3 to be irradiated onto a measurement-subject article M.
The measurement-subject article M reflects the laser beam L to produce a return light La which passes through the cover glass 3 to the inside of the casing 2. The return light La passes through the beam splitter 5, is then concentrated by the convex lens 6 and is then converted to parallel light by the concave lens 7.
When the normal of the measurement-subject article M is tilted (deflected) with respect to the axis a, a deflection occurs in the return light La. When this return light La is converted to parallel light by the concave lens 7, the deflection is increased.
Then the return light La passing through the concave lens 7 is reflected by the first reflection mirror 8 and then the second reflection mirror 9, and is then projected onto the verification screen 4.
The verification screen 4 displays the center point and a scale showing the degree of deflection from the center point. The center point is set at a light spot P produced by the return light La when no deflection occurs in the normal of the measurement-subject article M.
Accordingly, when deflection occurs in the normal of the measurement-subject article M due to mounting conditions or the like, the light spot P of the return light La appears in a position deviating from the center point of the verification screen 4, whereby the operator is able to detect the deflection of the normal of the measurement-subject article M.
The conventional auto-collimator 1 having the structure as described above uses two mirrors, the first reflection mirror 8 and the second reflection mirror 9. Therefore, the light path of the return light La from the concave lens 7 to the verification screen 4 is extended as compared with the case where the return light La directly enters the verification screen from the concave lens 7. Thereby, the deflection of the return light La is further increased. As a result, it is possible to detect the mounting conditions of the measurement-object article M with high accuracy.
However, when the deflection of a return light La is increased in this manner for an enhancement in accuracy of detection of the auto-collimator 1, even a slight deflection of the normal of a measurement-object article M causes the light spot P of the return light La to fall outside the verification screen 4, resulting in the problem of uncertainty about the direction in which to adjust the mounting position of the measurement-subject article M.